Exploring rich dark sectors for dark matter and neutrino masses with phenomenology at ICARUS

In this master’s thesis, realisations of rich dark sector models are proposed as a solution to the problems of dark matter and neutrino mass generation. In these models, sub-GeV dark photons Z′ can decay into final states with both visible and invisible particles. A variable number of heavy neutral particles ψi is postulated, which can be treated as dark matter (DM) candidates or heavy neutral leptons giving rise to neutrino masses via seesaw mechanism. After providing extensive context, the full mass spectrum is studied with the aim of reconstructing the Yukawa couplings from observed neutrino parameters. The models are then interpreted as variations of inelastic DM (iDM) and the case is made for their testability at ICARUS experiment, in its current operation in the Fermilab Short-Baseline Neutrino program, through the decay chain Z ′ → ψ1 (ψ2 → ψ1 l+ l− ), with the Z′ produced in rare neutral kaon decays. The parameter space region probed by this experiment is confronted with the cosmological range required for iDM. A Monte Carlo simulation (written using the Pythia generator and a combination of Mathematica and Python codes) was run to calculate the expected number of events in the detector. The simulation accounts for production, propagation and decay in the laboratory frame, taking into account the calculated decay rates and the geometry of the experimental setup.